The invention refers to a device which automatically cuts out non-essential loads in a generator and storagebattery fed electric circuit when the overall load on the circuit absorbs more power than the power fed by the generator to the battery, in order to prevent the battery charge from sinking below a critical level, i.e. the level below which the battery would become irremediably damaged.
The invention has its main field of application in motor vehicles, to whose electric circuits there are applied additional, non-essential fixtures such as air conditioners, electrically heated windows, a refrigerator etc.
The power plant of modern motor craft is designed to handle under normal operating conditions such additional loads without letting the charge of the storage battery sink below this critical level. However, conditions may occur in which, because of the simultaneous insertion of too many loads into the circuit or because of a reduction in the generator output, the electric power absorbed from the storage battery may exceed the power supplied to it by the generator and consequently its charge may sink to a level where the battery is irreparably damaged.
It is true that the electric plant of today's motor vehicles is provided with a warning lamp which lights up when the generator delivers to the storage battery no power or insufficient power because it stands still, is defective or runs at low speed, thereby signalling to reduce the loads on the electric plant of the vehicle. But there occur also conditions, in which the generator, although operating at full capacity, is still unable to deliver to the battery all the power absorbed therefrom by the loads. In this case, the warning lamp gives no warning, even after the battery has been discharged beyond the critical level, beneath which it becomes irreparably damaged.
The invention provides a device which automatically switches the non-essential loads off the electric circuit of a motor vehicle in those conditions in which the power absorption of the circuit exceeds the available power supply from the generator and switches them on again when these conditions cease.